Heating apparatus utilizing microwaves

Abstract: A heating apparatus utilizing microwaves characterized in that it is possible to heat with a super high temperature over about 1000°C and also to control the temperature within the wide range from such a super high temperature to a comparative low temperature. The heating apparatus is composed of a heating element (1) mainly made of a carbon powder and sintered in honeycomb structure, a microwave generator (2) irradiating microwaves to the heating element (1) and an air blower (8) blowing air to the heating element thereby obtaining hot air with high temperature.

Description: BACKGROUND OF THE INVENTION The present invention relates to the heating apparatus utilizing microwaves which is the most suitable especially for generating a hot air, for re-burning and purifying such as exhaust gas, for burning an inflammable thing and for heating objects to be heated, see GB-A- 2 231 762. Hitherto, there has been widely known a hot air electric heater with nichrome wire or a gas hot air heater using gas, etc. as a heating apparatus generating a hot air. Those hot air electric heater and gas hot air heater, however, could not easily heat to the temperature as high as 1000°C or over. Further, there have been some apparatus burning an object to be burned utilizing microwaves such as JP-A-4-301122 and JP-A-4-298623, etc. which mainly consist of filters, ceramics of honeycomb structure, a microwave generator and a waveguide. These apparatus are used to burn the particulates (very minute parts) included in the exhaust gas which generate from the internal combustion engine. The particulates are caught by the filter and are burned with microwaves. The filter and the ceramics of honeycomb structure including the microwave absorption materials will be heated by being irradiated with microwaves but not to the temperature as high as 1000°C or over because usual microwave absorption materials are not stably heated to such a high temperature. The object of these apparatus is to burn the particulates (very minute parts) of the exhaust gas, which are caught by the filter, directly with microwaves. The remains or the exhaust gas not caught by the filter will be exhausted without being purified and even the particulates caught by the filter may not be burned completely because the filter is not heated to such a high temperature as 1000°C or over. SUMMARY OF THE INVENTION The present invention can heat to the temperature as super high as 1000°C or over and the object of the present invention is to provide a heating apparatus which can control the temperature within the wide range or from super high temperature (about 2000°C) to relatively low temperature (about 30°C). A heating element of the present invention absorbing microwaves heats to high temperature by being irradiated with microwaves and can heat the object to be heated to such high temperature. Being formed in the honeycomb structure, the heating element obtains high efficiency of heat exchange. Further it is possible to control the temperature in the wide range of from high temperature to low temperature by controlling the output of an electromagnetic microwave generator. The heating element which is mainly made of carbon powder heats to the high temperature by being irradiated with a microwave and heats the gas, for example, such as air or exhaust gas, etc. to touch with to the high temperature. The said gas, etc. pass through the heating element contacting its surface very closely and are heated to the high temperature with high efficiency of heat exchange due to the honeycomb structure of the heating element. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic side sectional view showing a super high temperature heating apparatus of one embodiment of the present invention. Fig. 2 is a front view showing a heating element with honeycomb structure in Fig. 1, and Fig. 3 is a schematic side sectional view showing an exhaust gas purifying apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENT One embodiment of the present invention will be explained with reference to the attached drawings hereinafter. Fig. 1 shows a super high temperature heating apparatus of one embodiment of the present invention. A heating element with honeycomb structure 1 shown in Figs. 1 and 2 generates high temperature by being irradiated through a waveguide 3 with microwaves generated by a magnetron 2 which generates microwaves of 2450 MHz. The heating element with honeycomb structure 1 is mainly made of a carbon powder in which an aluminum powder can be mixed. If the microwave having high frequency about 2450 MHz ordinary used for an electronic range or the like is irradiated to the heating element 1, the carbon powder is mainly heated due to a dielectric heating function till a high temperature. By adjusting a mixture ratio of the carbon powder and the aluminum powder, it is possible to adjust the generated temperature within a range from about 30°C to about 2000°C. As mentioned above, the temperature of the heating element is changed in accordance with the mixture ratio, and the following table shows the experiment results showing the relationship between the lapse time in which the mixture with about 3 gr, is heated to the temperature within the range from about 600°C to about 700°C and the mixture ratio (volume ratio). As is apparent from the above table, if there is no aluminum powder, the heating element reaches to the above high temperature 600°C to about 700°C in only one minute, but as the aluminium powder is increased, the time required to reach the predetermined temperature is also increased. This means that the aluminium powder functions to restrict an abrupt increment of temperature of the heating element and to retain the high temperature of the heating element. Furthermore, if the amount of the aluminium powder is increased rather than the amount of the carbon powder, not only there is obtained a later increasing speed in temperature but also the obtained temperature may be restricted to about 400°C to 500°C. The heating element with honeycomb structure 1 can be made by sinter forging process using moulding blocks under the high temperature and the high pressure and has many beehive-like small penetrating holes in the inside. It is possible to make the heating element with honeycomb structure of about 100 mm in diameter with many penetrating holes, of which one is about 1 mm in diameter by about 20 mm long. The section of a penetrating hole can be formed in any shape such as a round, a logenze, a rectangle, a hexagon, a triangle, etc. The magnetron 2 is supplied with electric power from sources of electricity using a transformer 4 and a condensor 5. The heating element with honeycomb structure 1 is covered with an adiabatic material 6 on its outside. An air blower 8 blows the wind into the heating element 1. A mesh filter 7 to prevent the leakage of microwaves is equipped in front of and at the back of the heating element with honeycomb structure 1. Microwaves generated by a magnetron 2 are irradiated to the heating element with honeycomb structure 1 from the outside to the center. The air heated by the heating element with honeycomb structure 1 is heated to maximum about 2000°C. Accordingly a super high temperature heating apparatus generating the hot air of such a high temperature as above-mentioned can be used for a fan-heater, a drier, a desiccator, an exhaust gas purifying apparatus, an oil cleaner, a separator of water and oil, a combustion furnace, etc. The temperature of the heating element 1 can be controlled by adjusting the volume of irradiation of microwaves generated by the magnetron 2. Fig. 3 shows an exhaust gas purifying apparatus which is another embodiment of the present invention. For example, exhaust gas generated from an internal combustion engine comes from the bottom, passes through the cylindrical exhaust gas purifying apparatus and goes out from the upper part. There is packed a heating element A or a heating element B in the inside of the exhaust gas purifying apparatus. As mentioned in the first embodiment, a microwave generated by the magnetron 2 is irradiated through a waveguide 3 to a heating element A or B which is heated to about 1350°C. The heating element A is similar to the heating element with honeycomb structure above-mentioned and has many straight penetrating holes. Exhaust gas moves straight through penetrating holes of the heating element A. The heating element B has many winding holes. This offers the increasing high efficiency in wasting and purifying the exhaust gas because the exhaust gas stays in the holes longer and is heated longer due to winding holes. The exhaust gas is heated to the high temperature by contacting with the heating element A or B of high temperature and as a result, an inflammable constituent of the exhaust gas burns and a nitrogen oxide and a stink constituent, etc. are eliminated. There is equipped a mesh filter 7 to prevent the leakage of microwaves on the heating element. Water is supplied automatically from a water supply device (not shown) which is set above the exhaust gas purifying apparatus. Vapor jets from minute holes of the mesh 10 and mingles with the exhaust gas. Such a mixture is utilized to eliminate a nitrogen oxide. While the exhaust gas goes through the heating element A or B, an inflammable constituent of the exhaust gas burns, and a stink, etc. can be eliminated. Materials to prevent a thermal oxidation can be coated on the surface of the heating element 1. That is to say, the heating element 1 is coated on the surface with the mixed solution which contains minute powders of metal oxide or other heat-resistance materials and then is dried to evaporate a solvent of the mixed solution. And accordingly materials to prevent a thermal oxidation cover the surface of the heating element 1. The covering with a thickness of about 20 micron or more is the most ideal for the materials to prevent a thermal oxidation. There are zirconium, aluminium, silica, nitriding aluminium, etc. as a metal oxide and heat-resistance temperatures of these materials are 2600°C, 2050°C, 1760°C and 2700°C - 2800°C respectively. One of the means to prevent an oxidation of a carbon or of a mixture of a carbon and an aluminium is to mix a silicon carbide powder with a carbon powder or an aluminium powder. If carbon powders are oxidized, they will be covered with oxide membranes. As a result, a combination of carbon powders themselves or a combination of carbon powders and aluminium powders will grow weak. It also causes that a honeycomb structure sintered under a high temperature and a high pressure is easily deformed. To prevent such an oxidation, it is effective to mix a silicon carbide powder with a carbon powder or with a mixture of a carbon powder and an aluminium powder. Furthermore, as explained in the example of the aluminium powder above-mentioned, it is possible to get a later and stable increasing speed in temperature. The following table shows the experiment results showing the relationship between the lapse time in which the mixture is heated to the temperature within the range from about 600°C to 700°C and the mixture ratio (volume ratio) of the carbon powder, the aluminium powder and the silicon carbide powder. As mentioned above, according to the present invention, high temperature is easily and quickly obtained by utilizing a heating element with high temperature generated very efficiently due to the irradiation of microwaves. Therefore not only a hot air for the heater or the dryer but also a hot blast with high temperature for the combustion of the inflammable thing are easily obtained. Further it is possible to waste and purify the exhaust gas quickly. It is possible to dry and burn the garbages discharged from, for example, the restaurants, the hospitals and the home, etc. and to destroy by fire bubbled polystyrenes, etc. The heating element of the present invention can be used with microwaves in the wide applications as the supply source of the heating for a refrigerator or a cooling apparatus, a fan hater for the room heating, a washing and drying machine, a separator of water and oil, a water heating apparatus, a solution heating apparatus, a sterilizer a cooking apparatus, etc. because it is possible to and control the temperature in the wide range of from high temperature (about 2000°C) to low temperature (tens of degree in Celcius).

Claims: A heating apparatus utilizing microwave and comprising a heating element (1); a microwave generator (2) for irradiating microwaves to said heating element (1) and an air blower (8) for blowing air over said heating element (1); characterised in that said heating element (1) is mainly made of carbon powder sintered in a honeycomb structure. A heating apparatus according to claim 1, wherein said heating element (1) contains carbon powder and aluminium powder. A heating apparatus according to claim 1, wherein said heating element (1) contains carbon powder, aluminium powder and silicon carbide powder. A heating apparatus utilizing microwaves according to claim 1, 2 or 3 wherein the surface of said heating element (1) is covered with membranes to prevent thermal oxidation. A heating apparatus utilizing microwave and comprising a heating element; a microwave generator (2) irradiating microwaves to said heating element (1); and means for supplying exhaust gas to said heating element (1) to be purified by said heating element (1) at a high temperature; characterized in that said heating element (1) is mainly made of carbon powder sintered in honeycomb structure. A heating apparatus according to claim 5, wherein said heating element (1) contains carbon powder and aluminium powder. A heating apparatus according to claim 5, wherein said heating element (1) contains carbon powder, aluminium powder and silicon carbide powder. A heating apparatus utilizing microwaves according to claim 5, 6 or 7 wherein the surface of said heating element (1) is covered with membranes to prevent thermal oxidation.

Inventors: NARA AKIKAZU, NARA, AKIKAZU
Applicants: NARA SEIKI KK, NARASEIKI KABUSHIKI KAISHA
Application year: 1994
Main classification: F24H3
IPC codes: F23G5, H05B6, F24H3, F23G7